1. Field of the Invention
The present invention relates to a liquid crystal display device and a video display device, and particularly to a liquid crystal display device and a video display device having a liquid crystal panel that can suppress degradation in display characteristics in the liquid crystal panel.
2. Description of the Related Art
A projection type video display device such as a liquid crystal projector or the like separates light emitted from a light source into red, green, and blue, modulates the pieces of color light by three light valves formed by a liquid crystal display element, synthesizes color luminous fluxes after the modulation, and then enlarges and projects resulting light onto a projection surface.
Such a video display device has recently been desired to have higher luminance and longer life. In order to achieve both higher luminance and longer life, a liquid crystal display element using an alignment film formed by an inorganic material that is not degraded under intense light has been applied.
A liquid crystal panel for forming the video display device is formed by interposing a liquid crystal layer between a first substrate and a second substrate arranged so as to face each other. A common electrode is provided on an opposed surface side of a pixel area (effective pixel area) of the first substrate and on the entire surface of an opposed surface side of the second substrate.
The electrodes are covered by respective alignment films. These alignment films control the state of alignment of liquid crystal molecules included in the liquid crystal layer.
Further, a gap between the first substrate and the second substrate is sealed by a seal material provided in a peripheral area around the pixel area, so that the liquid crystal layer is filled and sealed in between the first substrate and the second substrate.
It is known that an ionic impurity mixed in at a time of injection of the liquid crystal or eluted from the seal material surrounding the liquid crystal layer in the liquid crystal panel formed as described above is diffused into the pixel area and aggregated by the subsequent driving of the liquid crystal display device, so that display characteristics of the liquid crystal panel are degraded.
Accordingly display devices of various constitutions intended to suppress degradation in such display characteristics have been proposed.
For example, Japanese Patent Laid-Open No. Hei 10-260406 (hereinafter referred to as Patent Document 1) proposes the following. A display device in which using surface modification by ultraviolet-ray irradiation, the surface energy of an alignment film situated in a peripheral area is set higher than the surface energy of an alignment film in a pixel area situated in a central part of a liquid crystal panel, so that an ionic impurity eluted from a seal material is adsorbed and captured in the alignment film part of the peripheral area having higher surface energy and thereby diffusion of the ionic impurity into the pixel area is suppressed.
In addition, Japanese Patent Laid-Open No. Hei 3-152512 proposes a display device in which a material having high ion adsorptivity is provided in a peripheral area to thereby suppress diffusion of an ionic impurity into a pixel area as in Patent Document 1.
Further, Japanese Patent Laid-Open No. Hei 10-177177 proposes a display device that has a barrier structure for preventing diffusion of an ionic impurity eluted from a seal material, in which structure a projection is provided between the seal material and a pixel area.
Further, a large number of display devices that have an ion trap electrode in a peripheral area to adsorb impurity ions electrically and thereby suppress the diffusion of the impurity ions have been proposed. See, Japanese Patent Laid-Open No. Hei 1-293317, Japanese Patent Laid-Open No. Hei 4-125617, Japanese Patent Laid-Open No. Hei 6-289408, Japanese Patent Laid-Open No. Hei 8-201830, Japanese Patent Laid-Open No. Hei 9-54325, Japanese Patent Laid-Open No. 2000-338510, Japanese Patent Laid-Open No. 2002-196355, Japanese Patent Laid-Open No. Hei 4-86812 (hereinafter referred to as Patent Document 11), and Japanese Patent Laid-Open No. 2006-47613 (hereinafter referred to as Patent Document 12).